A dark nebula that runs along the local spiral arm of our Galaxy, dividing the Milky Way. It starts in Cygnus, where it is also known as the Cygnus Rift or Northern Coalsack, and can be traced south through Aquila into Ophiuchus, where it broadens out. It consists of a large group of molecular clouds approximately 2200 l.y. away, containing almost 1 million solar masses of gas. The clouds of gas and dust extend for over 1000 l.y.